The present invention relates to semiconductor manufacturing equipment and particularly to a cleaning system for spin stations used to apply photoresist to semiconductor wafers.
An integrated circuit may contain millions of circuit elements which cannot be fabricated by any physical tool. Instead, the photolithography process--using optical images and a photosensitive film called photoresist--is used to produce the desired circuit patterns on the semiconductor wafer. The process requires one or more applications of the photoresist (resist) to the wafer to be selectively exposed. As shown in FIG. 1, a spin station 2 is used to apply the resist on the surface of the wafer by dispensing the resist on the wafer and then spinning the wafer at high rpm. The spin station 2 typically includes a member such as a spin chuck 10 for holding and rotating the wafer W and a spindle 16 connected to a motor (not shown) for rotating the spin chuck 10. The spin station 2 also includes a catch cup consisting of, for example, a top 12, a bottom 14, and a shield 18 for housing the wafer W on the spin chuck 10, and a dispensing member such as a nozzle 20 for applying the resist to the wafer W. During the spin-coating process, the spinning of the chuck 10 quickly rotates the wafer W to a high rpm, which spreads the resist across the surface of the wafer and rids the excess resist off the wafer by centrifugal force.
Clean air is directed through the spin station 2 to control the temperature and humidity of the environment in the catch cup. Because the resist typically includes a high concentration of volatile solvents, the resist will quickly dry and adhere to the inner walls of the catch cup before it can drain from the bottom 14 of the catch cup. The resist will deposit on the inner walls of the top 12, the bottom 14, and the shield 18 of the catch cup. After even a few processing cycles, excessive amounts of resist can begin to accumulate on the inner walls of the catch cup. This build up of resist on the inner walls of the catch cup can alter the desired air flow characteristics around the wafer and can lead to wafer contamination and poor coating uniformity.
In an attempt to avoid these types of problems, semiconductors manufacturers have removed the catch cup from the spin station and manually applied cleaning fluids to the contaminated inner surfaces of the catch cup. However, this is a labor intensive operation and removes the spin station from production for a long period of time. Other manufacturers have attempted to clean the catch cup by rotating the catch cup while a cleaning nozzle, fixed in position relative to the rotating catch cup, dispenses cleaning fluid or solvent on the contaminated inner walls of the catch cup. Rotating the catch cup, however, increases the complexity of the spin station by requiring that the catch cup which was formerly stationary now rotate for cleaning and be driven by an additional motor.
Others have attempted to avoid these problems by providing a cleaning system as shown in FIG. 2. In this system, a plate 27 is placed on a spin chuck 26 and a set of backside edge bead removal nozzles 28 provided below the plate 27 to supply cleaning fluid to the bottom edge of the plate 27. During the spinning of the spin chuck 26, the cleaning fluid exits the plate 27 through a set of holes 21 arranged at various angles with respect to the plate 27 to direct cleaning fluid to the inner walls of the catch cup top 30. Because the holes 21 are arranged at different angles with respect to the direction of the cleaning fluid exiting the nozzle 28, the velocity in which the cleaning fluid exits the plate 27 is not uniform. The centrifugal force favors the fluid direction which is planar to the plate 27. This leads to inadequate cleaning of the inner wall of the catch cup top 30 and no cleaning of the outer wall of the catch cup shield 32. The inability of the cleaning fluid to reach the catch cup shield 32 then requires that the catch cup be removed and manually cleaned. Because the distance from where the cleaning fluid enters and exits the plate 27 is very small, and because the fluid relies only on the centrifugal force of the spin chuck 26, the cleaning fluid velocity and pressure is not high enough to effectively remove the resist on all the desired surfaces. This requires the spindle 29 to move up and down during the cleaning operation in an attempt to reach all of the inner surfaces of the catch cup.
Another attempt to solve these types of problems includes injecting cleaning fluid into the catch cup through small holes in the top of the catch cup so that cleaning fluid drips down the inner walls of the catch cup before the wafer is coated with resist in an attempt to prevent the resist from ever adhering to the walls of the catch cup. Another attempt uses multiple high pressure jets to supply cleaning fluid without the use of the rotating plate. Either of these attempts use large amounts of cleaning fluid and some customers consider the high pressurized system necessary for jetting the cleaning fluid as inherently unsafe.
It would be highly desirable to provide a catch cup cleaning system which can be used with a variety of spin stations, is highly automated, is capable of directing cleaning fluid at all of the areas where resist builds up in the catch cup, does not require removal of the catch cup, takes advantage of existing components in the spin station, and reduces the consumption of the cleaning fluid.